The present invention relates generally to a machine for joining two members at a miter joint, a clamping head assembly for use in such a machine, and a method of retrofitting an existing joining machine to include the present clamping head assembly. More particularly, the preferred embodiment of the present invention relates to a frame making machine used for joining two frame members at a miter joint, where the machine includes a clamping head assembly with two fence members, at least one of which is movable, which are used to align the frame members in the proper orientation. The present invention also relates to such a clamping head assembly, as well as to retrofitting a machine that includes a conventional head assembly with the present head assembly. It should be noted that although the preferred embodiments of the present invention will be shown and described as being intended for use in the frame making industry, uses of the present invention in other industries that require members to be joined together at a miter joint are also contemplated as being within the scope of the invention, for example the woodworking industry.
A miter joint is a corner joint formed by fitting two members together at their respective edges, wherein each edge is cut at some angle; the line defined at the joint between the adjacent edges is the miter angle. Conventionally, for adjacent edges cut at the same angle, if the included angle between the two members is 90 degrees, the miter angle will be 45 degrees, and if the included angle is 60 degrees, the miter angle will be 30 degrees. Therefore, a miter angle by definition is an oblique angle.
Machines for joining two frame members at a miter joint are known in the art. One popular machine, which is shown in an exploded view in FIG. 1, is the xe2x80x9cMitre-Mite VN 4 Electronic,xe2x80x9d which is manufactured and distributed by Alfamachine-ITW/AMP of Vernon Hills, Ill. The frame making machine 10 includes a work table 12 with a preferably horizontal work surface 14. Briefly, as known to those of ordinary skill in the art, the machine 10 operates as follows. First, one frame member is aligned along each one of the two fence members (22, 24) with a miter joint therebetween. Next, the frontal clamp 18 (optional) moves horizontally in a direction that is generally coincident with the miter joint, and pushes each of the two frame members against its respective fence member (22, 24). Third, the vertical clamp (20) engages the frame members from the top, pushing them downwardly against the work surface 14. Finally, the two frame members are nailed together at the miter joint by one or more nails (e.g., V-nails, corrugated fasteners or other fasteners) that are driven upwardly into the miter joint from a nail driving mechanism that is seated below the work surface 14. After the nailing operation, the two frame members (which are now a single unit) can be removed from the machine since they have been joined together at the miter joint.
Since the present invention relates primarily to the methods and apparatuses used to clamp the frame members in place, these features of the prior art machine will be described next in more detail. The machine 10 includes three primary clamping subassemblies: (1) a stationary clamping assembly 16; (2) a movable frontal clamp assembly 18; and (3) a movable vertical clamp assembly 20. It should be noted that since these features are known to those of ordinary skill in the art, only the major components of each subassembly will be described below.
The stationary clamping assembly consists primarily of two stationary fence members 22 and 24 that are relatively rigidly affixed to the work surface 14 by a plurality of screws 26 extending through a plurality of associated holes 28. The holes 28 are in the form of elongated slots to allow for some adjustment of the positioning of the stationary fence members 22, 24. Knobs 30 are useful for adjusting the vertical angle of the edge of the fence members to better accommodate and achieve a tight fit between frame members having angled or non-uniform edges. A shown in the FIG. 1 view, the inner (or left) side of each of the stationary fence members defines a positioning edge upon which a respective edge of one of the frame members intended to be joined together is seated against.
The second subassembly, the movable frontal clamp assembly 18, includes a movable frontal clamp member 32, which is configured to move within track 34. The position of the frontal clamp member 32 may be varied by moving the securing knob 36 to another one of the holes 38. In operation, the movable front clamp member 32 is moved from a first position in which it is drawn backward (toward the left-hand side of FIG. 1) to a second position (toward the right-hand side of FIG. 1) in which it is clamping against the frame members intended to be joined together. The direction of travel of the frontal clamp member 32 is essentially coincident with the miter between the two frame members being joined together.
The third subassembly, the movable vertical clamp assembly 20, includes a pressure plate 37 that is attached to a rod 39. The rod 39 is attached to a support structure 40, which is in turn connected to two cylinders 42. The cylinders 42 are rigidly affixed to the work surface 14 from below so that the attachment plates 44 are below the work surface 14 and the cylinders 42 extend through holes 45 to be situated above the work surface. If necessary, the horizontal location of the pressure plate 37 may be adjusted by loosening handle 46, and then sliding the threaded dowel 48 within the slot 50. The vertical height of the pressure plate 37 may be adjusted by manipulating the other handle 52. In operation, the cylinders 42 are withdrawn to push the pressure plate 37 downwardly upon the top of the frame members being joined together at the miter joint. In this manner, the frame members are firmly held down when the fastener(s) (e.g., V-nails, corrugated fasteners) are inserted from below.
One common problem with many frame assembly machines of the prior art, such as the one described above, is that the two frame members being joined together may not be properly held together at the miter joint. There may be a slight space between the two frame members at the miter joint prior to nailing. If this is the case, when the frame members are nailed together, there will be an unsightly gap between the two frame members at the joint. That is, the miter joint may be too wide along its entire length, resulting in a visible air space along the entire length of the miter joint, or the miter joint may be uneven, whereby a portion of the joint has a visible air space and another portion is tight with no visible air space. Neither of these two situations is desirable since the intent is to arrive at a tight miter joint with no visible gap between the two frame members.
Accordingly, one object of the present invention is to provide an improved frame assembly machine which is capable of consistently making a tight miter joint.
Another object of the present invention is to provide a clamping head assembly for use with a frame assembly machine whereby the resulting miter joints are tight.
A third object of the present invention is to provide a clamping head assembly for use with a frame machine where the assembly includes at least one movable fence member for properly positioning the frame member within the machine prior to the nailing operation.
A fourth object of the present invention is to provide a clamping head assembly that applies a force to the frame members being joined together at a miter joint, where that force is applied in a direction that is approximately perpendicular to the miter joint.
An additional object of the present invention is to provide a method of retrofitting an improved clamping head assembly upon an existing frame assembly machine.
These and other objects of the present invention are discussed or will be apparent from the following detailed description of the present invention.
The above-listed objects are met or exceeded by the present frame assembly machine, which features a clamping head assembly that provides an additional clamping force for maintaining the frame members in position prior to being joined together at a miter joint, where that additional clamping force is applied in a direction that is approximately perpendicular to the miter joint. In the preferred embodiments, the additional clamping force is realized by providing a movable fence member that cooperates with a stationary fence member to retain the two frame members in the proper position prior to being nailed together.
More specifically, the present invention provides a clamping head assembly for clamping a first member to a second member at a miter joint, where the clamping head assembly includes a first fence member with a first positioning edge for positioning an edge of the first member and a second fence member that is movable and includes a second positioning edge for positioning an edge of the second member. The second positioning edge is arranged at an approximately right angle with respect to the first positioning edge. Additionally, the first fence member and the second fence member are configured and arranged to that the approximately right angle is approximately bisected by the miter joint formed between the first and second members. The second fence member is movable in a direction that is approximately perpendicular to the miter joint, whereby a normal force is generated upon the miter joint. Furthermore, the present invention also relates to a frame making machine that includes the clamping head assembly just described.
Another aspect of the present invention relates to retrofitting an existing frame making machine with an improved clamping head assembly. In particular, the invention relates to a method of retrofitting a frame making machine that originally includes a primary work surface (preferably generally horizontal) and two stationary fence members for positioning first and second frame members intended to be joined together at a miter joint, where the two stationary fence members are seated upon the primary work surface. The first step of the method involves removing at least one of the stationary fence members from the frame making machine. The second step involves installing at least one movable fence member upon the frame making machine, where the movable fence member is capable of being moved in a direction that is generally perpendicular to the miter joint between the first and second frame members.